Inertia rate of fire retarders



Oct. 19 1948. c. c. LOOMIS EI'AL 2,451,624

INER'TIA RATE OF FIRE RETARDERS- Filed Aug. 27, 1947 2 sheets-sheet 1 YEW Patented Oct. 19, 1948 UNITED STATE TENT 'EFICE INERTIA RATE OF FIRE RETARDERS Application August27, 1947, Serial N0. 770.878

.6 Claims.

actions.

It is an object of this invention to modify the time-displacement characteristics of the automatically operating parts in a manner which will improve the certainty of functioning. Of particular interest is the provision'of an operating cycle which insures that cartridges will have an adequate period of time in which to feed to a loading position.

It is contemplated that this object may be best accomplished by providing a spring mounted inertia Weight which, in accordance with the wellknown laws of motion, resists any force tending to disturb its condition of motion. Such an-inertia block operates to delay commencement of the rearward movement of a part such as a breech bolt and to insure that there will be a slight pause at the rearward position thereof before returning under spring force to a normal forward position. The pause in rearward position is of particular significance when the invention is applied to a breech bolt, for it permits adequate time for a fresh cartridge to feed up to a loading position in front of the bolt.

The exact nature of the invention, as well as other objects and advantages thereof, will be more clearly understood from consideration of a detailed specification referring to the accompanying drawing, in which:

Figure 1 is a side elevational view partly in section, showing a typical firearm provided with one embodiment of our invention. The mechanism is shown in a normal breech closed position.

Figure 2 is a partial sectional view illustrating the position of the inertia block at an instant corresponding to that just after the firing of a cartridge or just after restoration of the breech mechanism to a forward position after the firing of a round.

Figure 3 is a partial sectional view corresponding to'Figure 2 but showing the relative positions of the parts at the rearward end of the cycle of movement.

Figure 4 is a composite graph comparing the time displacement curves of two otherwise identical firearms, one of which is equipped with this invention. The dotted line curve shows the characteristics of the unmodified firearm. In this curve, displacements in inches are plotted as ordinates and time in milliseconds as the abscissa.

Referring to the drawing, it will be seen that it illustrates the application of our invention to a firearm of .the type of the U. S. rifle caliber .30 'M-l, shown generally in U. S. PatentNo. 2,327 .338 to John C. Garand, or a modified form of that rifle which is the subject or our patentapplication, Serial Number 770,87 9, filed August 27, 1947. The modified form is adapted to function as a full automatic rifle or it may be adjusted to fire on the same semi-automatic cycle as the rifle of the Garand patent.

The rifles to' which our invention is shown applied are of the gas-operated type and provide for bleeding gas from the barrel through a port I in proximity to the muzzle. The tapped gas is led intoa gas cylinder 2 where its expansion serves to drive rearwardly a piston 3 which is formed integrally with an operating rod 4. As shown in detail in the Garand patent, a suit-able cam formed in a portion '5 of the operating rod engages a lug on the bolt 7 to impart rotation and translation thereto. An operating spring 8 is engaged between a relatively fixed spring guide rod 9 and acts on the operating red to normally urge it to occupy a forward position.

In the rifle of the Garand patent, the spring 8 acts directly on the inside of the head of the gas piston 3. In our invention there is interposed between the spring 8 and the piston 3 an inertia block or retarder 1B which is necked down as at H to receivethe forward end of the operating spring 8 and a relatively heavy retarder spring !2 mounted on a necked portion 1 3 of the retarder Hi and extending forwardly therefrom into contact with the head of the piston 3. If our invention is applied directly to the standard military rifle, the

original operating spring may still be utilized if its seat is moved rearwardly on the spring guide 9 by an amount equal to the length of the retarder l8 and spring l2.

In all other respects, the rifle may be either the standard M-l rifle or the modified version which is the subject of our application above referred to. Obviously, the'utility of the invention is more outstanding in connection with full automatic operation.

Considering first theaction'of the rifle on the firing of a first round, which also corresponds to the condition of firing for succeeding rounds during semi-automatic operation, it will be realized that there is a natural tendency for the gun, as a whole, to recoil rearwardly. In this rear- Ward movement, all parts which are not restrained against relative forward movement must participate. The retarder 10, it will be observed, is not so restrained and as the operating rod 3 recoils with the barrel, the retarder tends to remain in its original position and to compress the retarder spring II. At about the time that the retarder spring is at its maximum compression, gas enters the cylinder 2 and drives the piston to the rear to operate the action. This movement is, however, slightly delayed for the compression of the spring H and the inertia of the retarder l must be overcome before the operating rod can commence to move relative to the cylinder. Figure 2 illustrates the relative position of the parts.

As the operating rod moves rearwardly, the two opposing springs tend to balance and the retarder assumes substantially its normal position relative to the gas piston. However, when the operating rod reaches its rearward position, it is stopped abruptly and the retarder, having considerable velocity, continues to the rear, compressing the operating spring 8 and pulling the retarder spring ll completely out of contact with the gas piston. This is the position of the parts as they are seen in Figure 3. Due to the elasticity of the contacting metallic surfaces, the operating rod tends to rebound forwardly but such movement is opposed by friction and by residual gas pressure in the gas cylinder. Since the effect of the retarder has been to remove for the moment the returning action of the spring 8, the operating rod comes to a virtual standstill near its rearmost position. This condition persists until the momentum of the retarder has been overcome and the compressed operating spring has moved the retarder spring back into contact with the head of the gas piston. During this pause the face of the bolt is in a position to the rear of that in which it engages the uppermost cartridge in the magazine and ample time is thus allowed for the magazine spring to assert itself and move the cartridge into its uppermost position, where it will be positively engaged by the bolt face and fed to the chamber.

The action of the retarder on the forward stroke is of more significance in connection with full automatic operation than in connection with semi-automatic operation. To better understand the reason for this, it may be noted that the modified rifle shown in our application above referred to is arranged in such a fashion that the final portion of forward movement of the operating rod brings a surface M on the operating rod into contact with the end of a firing bar to initiate the firing of the round chambered and locked in place by the preceding part of the forward movement of the operating rod. At or shortly after the time of actual firing of the cartridge, the operating rod reaches its foremost position and the retarder which is moving with considerable velocity compresses the retarder spring almost, if not entirely, to its solid length.

The peak of this compression is reached at about or shortly after the time the gas from the barrel is bled into the gas cylinder and the initiation of rearward movement is delayed materially by the forward momentum of the retarder spring. The opening of the bolt is thus delayed with the effect of reducing the rate of fire and with the additional effect of permitting extraction at lower breech pressures.

Obviously, retarders of different weights will have somewhat different effects. The actual weights used in one typical example which will be further discussed hereinafter were as follows:

Grams Operating rod 285 Operating spring 60.7 Bolt 154.5 Retarder 56.2 Retarder spring -i 4.2

The time displacement curves shown in Figure 4 were obtained by the analysis of high speed motion pictures upon which an accurate time signal had been superimposed. The rifle was the same in the case of each curve, the dotted line curve indicating the characteristics when the retarder and retarder spring were removed. The condition represented is full automatic fire and the time zero in each case is the instant at which the operating rod returned to its foremost position after the firing of a preceding round, chambering, locking, and initiating the firing of the round for which the data is plotted. The curves have been corrected for the effect of recoil of the gun as a whole and. the displacements indicated are those of the operating rod relative to the receiver of the rifle.

Examining these curves in detail, it will be seen that the use of the retarder delayed the commencement of rearward movement of the operating rod for '7 milliseconds, as shown by the difference between the parts of the curve marked A and B. Although comparable breech pressure curves were not taken, it is obvious that the pressure acting inside the case at the time of extrac-- tion must have been materially less.

In the rifle which was tested, the bolt face rides over the rear end of a cartridge held in the magazine after an operating rod displacement of 4.1 inches. The time consumed [between this point on rearward and forward movement is allowed for the magazine spring to thrust the succeeding roundup in front of the bolt face for chambering. In the case of the rifle without the retarder, this interval marked C on the curve was only 4.8 milliseconds, which is barely enough as demonstrated by the occasional failure of the bolt to pick up the cartridge. Apparently, if in the course of the usual variations in ammunition, operating conditions, etc, this overtravel time is less than 4.8 milliseconds, there is quite apt to be a failure to feed.

In the case of the rifle equipped with the retarder, the overtravel time, shown as D, was nearly doubled to 9.3 milliseconds. It is quite apparent that after the initial slight rebound, the bolt came almost to a stop and that it was brought to a complete stop by contact with the head of the cartridge. When the operating spring again made its influence felt, the cartridge was smoothly accelerated and fed into the chamber.

A somewhat wavy condition of the sloping parts of the curves is believed to be due to spring surges and the difference in time consumed on the relatively straight line movements of the operating rod does not appear to be particularly significant. The total time consumed for one cycle without the retarder was 94 milliseconds, which corresponds to a cyclic rate of 640 rounds per minute as compared to 106 milliseconds or 565 rounds per minute when equipped with the retarder.

It is believed that the applicability of our invention to other firearm elements is apparent and accordingly, we do not wish to have our invention considered as limited by the exemplary disclosures made herein. The claims appended hereto are indicative of the limitations upon our invention.

We claim:

1. In a firearm having a movable member adapted to be forcibly moved during operation of the firearm and also having spring means to oppose such motion; rate modifying means comprising an inertia member mounted between the ends of the spring means for movement along a path substantially similar to that of the movable member, said inertia member being restrained from movement along said path only by engagement with said spring.

2. In a firearm having a movable member adapted to be forcibly moved during operation of the firearm and also having spring means to oppose such motion; rate modifying means comprising an inertia member in engagement with said spring means and a retarder spring bet-ween said inertia member and said movable member, said inertia member being guided for movement along substantially the same path as said movable member and being restrained along said path only by engagement between said springs.

3. In a firearm having a movable member which is impelled rearwardly in operation of the firearm and spring means to urge said member back to a forward position; rate modifying means comprising an inertia member engaging said spring means and a retarder spring engaged between said inertia member and the movable member, said inertia member being guided for movement along a path similar to that of the movable member and being restrained from movement along that path solely by engagement between said spring means and said retarder spring.

4. In combination with a firearm part adapted to be moved longitudinally in operation of the firearm, an assembly opposing longitudinal movement in one direction comprising a pair of com-.-

pression springs and an inertia member mounted between said springs, said assembly being en- -aged between the longitudinally movable part and a relatively fixed portion of the firearm, and said inertia member being restrained from movement longitudinally only by its engagement between said springs.

5. In a firearm having a hollow gas piston open at its rearward end and operatively coupled to a firearm lbreedh mechanism, an assembly opposing gas propelled movement of said piston partially enclosed by said hollow piston and engaged between the =closed end thereof and a relatively fixed portion of the firearm, said assembly comprising a series arrangement of a retarder spring and an operating spring having engaged between them an inertia member.

6. In a firearm having a hollow gas operating piston open at its rearward end and operatively coupled to a breech mechanism in a firearm receiver, an assembly opposing gas propelled movement of said piston engaged between the forward end of said piston and said firearm receiver, said assembly comprising in a longitudinally disposed arrangement a retarder spring, an inertia member and an operating spring, said retarder spring and inertia member being housed Within said piston and said inertia member being restrained from longitudinal movement therein only by engagement between said springs.

CRAWFORD C. LOOMIS. JANE A. LOWE, Administratrzx of the Estate of Kenneth J. Lowe,

Deceased.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,344,991 Cunningham June 29, 1920 2,101,862 MacGregor Dec. 14, 1937 

